For many years thermometers for accurately determining body temperature used mercury in a glass capillary tube. The time required for mercury thermometers to achieve body temperature, when inserted into a body orifice, was on the order of four minutes, an unduly extended period.
In recent years electronic thermometers, which provide rapid and accurate readings of body temperature, have supplanted mercury thermometers in hospitals and the like. Such electronic thermometers ordinarily use a probe at the end of which is located a temperature sensitive element, for example a thermistor. Ordinarily, the electronic thermometers provide a temperature readout in 25 to 40 seconds, depending on several variables. The thermometer includes circuits which compute a predicted final temperature, of the temperature sensitive element based on the the rate of temperature rise. The computation is made when the rate of temperature rise falls below a particular value. As a consequence, the elapsed time for a temperature prediction varies, providing some inconvenience in use.